bpf: Restrict kernel image access functions when the kernel is locked down

There are some bpf functions can be used to read kernel memory:
bpf_probe_read, bpf_probe_write_user and bpf_trace_printk.  These allow
private keys in kernel memory (e.g. the hibernation image signing key) to
be read by an eBPF program.  Prohibit those functions when the kernel is
locked down.

Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0057-bpf-Restrict-kernel-image-access-functions-when-the-.patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 6350f64d5aa40e45f6e6f45e5563205c08518221..8493b89e1196e646ddadb02d5b64ba8f315eb6f3 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -65,6 +65,11 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
 {
        int ret;
 
+       if (kernel_is_locked_down()) {
+               memset(dst, 0, size);
+               return -EPERM;
+       }
+
        ret = probe_kernel_read(dst, unsafe_ptr, size);
        if (unlikely(ret < 0))
                memset(dst, 0, size);
@@ -84,6 +89,9 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
 BPF_CALL_3(bpf_probe_write_user, void *, unsafe_ptr, const void *, src,
           u32, size)
 {
+       if (kernel_is_locked_down())
+               return -EPERM;
+
        /*
         * Ensure we're in user context which is safe for the helper to
         * run. This helper has no business in a kthread.
@@ -143,6 +151,9 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
        if (fmt[--fmt_size] != 0)
                return -EINVAL;
 
+       if (kernel_is_locked_down())
+               return __trace_printk(1, fmt, 0, 0, 0);
+
        /* check format string for allowed specifiers */
        for (i = 0; i < fmt_size; i++) {
                if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i]))